The present invention relates to grain-oriented silicon steel sheets having an easy magnetization axis &lt;100&gt; in the rolling direction of the steel sheets and &lt;110&gt; on the sheet surface.
Grain-oriented silicon steel sheets have been mainly used for iron core of electric apparatus, such as converter and the like as soft magnetic materials and in particular, it has been recently strongly demanded to increase the properties of the electric apparatus and the like, to make the size of said apparatus small and to make the noise lower and the electric steel sheets having more improved magnetic properties have been demanded in view of energy saving.
The magnetic properties of steel sheets are generally evaluated by both iron loss property and magnetization property. The improvement of magnetizing property (represented by the magnetic induction B.sub.10 value at a magnetizing force 1000 A/m) is particularly effective for increasing the designed magnetic induction and making the size of apparatus smaller. On the other hand, the improvement of the iron loss property (represented by iron loss W.sub.17/50 per 1 kg when being magnetized to 1.7T (Wb/m.sup.2) with 50 Hz) reduces the loss of heat energy when used as the electric apparatus and is effective in view of saving of consumed electric power. Since not only the magnetizing property but also the iron loss property can be improved by enhancing the orienting property of the products, that is by highly aligning the axis &lt;100&gt; of the crystal grains to the rolling direction, many investigations have been made particularly in this view and the products having B.sub.10 of more than 1.90T have been produced.
As well known, the iron loss is roughly classified into hysteresis loss and eddy current loss. As the physical factors influencing upon these losses, there are the purity and inner strain of the material other than the above described crystal orientation with respect to the hysteresis loss and there are the electric resistance (for example Si amount), sheet thickness and magnetic zone size (crystal grain size) of the steel sheet and the tension applied on the steel sheet with respect the eddy current loss. In usual grain-oriented silicon steel sheets, the eddy current loss is more than 3/4 of the total loss, so that it is more effective for reducing the total iron loss to reduce the eddy current loss than to reduce the hysteresis loss. Therefore, various attempts for reducing the eddy current loss have been made. As one of them, it has been proposed to increase Si content but when Si content is increased to 4.0%, the cold rolling ability is noticeably deteriorated, so that there is a limitation and such a means is not practical. As a means for applying tension on a steel sheet, a means utilizing a difference of thermal expansion coefficient between a base coating or a face coating and a base iron has been known but there is limitation in the tension obtained from the commercially utilized coating and there is also limitation in view of the uniformity, cohesion, appearance of the coating and the like and it is impossible to expect the satisfactory reduction of iron loss. It has been recently proposed to form scratches in perpendicular direction to the rolling direction on the surface of the produced sheet to make the magnetic zones fine whereby the eddy current loss is reduced. But, in this method, the effect may not be necessarily fully developed depending upon the shape, average crystal gain size and sheet thickness of the produced sheet and when a strain relief annealing is applied to the produced scratched sheet, the lowered iron loss is returned to the original unimproved value, so that this method is not practical.